Each variety of chile has a different level of heat. The Scoville Scale is the traditional method of measuring heat. Photo of green jalapeño, red Scotch bonnet and orange habanero chiles courtesy Ashley Foods.

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The Scoville Scale

The most common way to evaluate chile pungency is a simple taste test. This method, although quick and cost-effective, may leave the tester in some pain: one would be happy to “let Mikey eat it.” There are two other ways of testing pungency as well, the Scoville organoleptic test and high performance liquid chromatography.

In 1912, Wilbur Scoville (born Walter Lincoln Scoville, 1865-1942), a pharmacologist who worked for the large pharmaceutical manufacturer, Parke Davis (now a subsidiary of Pfizer), questioned how to determine the different heat levels of the wide variety of chiles. He developed the first systematic laboratory approach used to measure their pungency—a simple laboratory test.

Called the Scoville Organoleptic Test, human subjects taste a chile sample and evaluate how many parts of sugar water it takes to neutralize the heat of the chile so that its pungency is no longer noticeable. This dilution is called the Scoville Heat Unit. This procedure is more accurate than the taste test (“bite the chile”) technique and less expensive than more advanced laboratory techniques—although the measure of pungency is still subjective and depends on the taster’s palate and sensitivity to the capsaicin (the chemical compound that gives chiles their heat) that are responsible for pungency. (In addition, there are serious limits on how many samples a taster can handle within a reasonable time.)

Today, a sophisticated laboratory process called High Performance Liquid Chromatography or HPLC, measures the amount of capsaicinoids (capsaicin) in parts per million. In this procedure, chile pods are dried, then ground; the capsaicins are extracted, and the extract is analyzed for total heat present as well as the individual capsaicinoids present. This method is more costly than the Scoville test or the taste test but much more accurate. While the measurement is in ASTA pungency units, not Scoville units, the scores are often converted to approximate Scoville unit values.

The chart below rates chiles, with 0 being mildest and 10 highest heat.

Mild Heat: 0 to 5,000 SHUs

Medium Heat: 5,000 to 20,000 SHUs

Hot Heat: 20,000 to 70,000 SHUs

Extreme Heat: 70,000 to 30,000 SHUs*

*In recent years, new varieties have been discovered that far exceed 30,000 SHUs. The world’s hottest chile, the bhut jolokia from India, has been measured at 1 million SHUs.

The stated heat ranges vary because the capsaicin levels of chiles grown even from the same seeds will vary:

The capsaicin can vary considerably within a species—by a factor of 10 or more‚ depending on seed lineage, climate, even soil.

The original Scoville test is an organoleptic test on humans, so even measurements of the same sample can vary by 50%.

When one looks at a score, one generally doesn’t know if it is an original Scoville test or a more accurate High Pressure Liquid Chromatography test. That’s why numbers from different sources vary so widely.

Most chart data from The Pepper Encyclopedia by Dave De Witt, William Morrow & Company.

*Guinness Book of Records’ “hottest spice”: In February 2007, the bhut jolokia from India was named the world’s hottest. A naturally occurring chile hybrid native to the Assam region of northeastern India, Bhut jolokia means “Ghost Chile” in Assamese. Prior to this new designation, the Red Savina was considered the world’s hottest; then in April 2007 the Dorset Naga tested almost 60% higher 876,000 SHUs. Originating in Bangladesh, it is sold with a health warning.